Interleukin-7 receptor a chain (IL-7Ra) is a cytokine receptor subunit for IL-7 and thymic stromal lymphopoietin. IL-7R1-derived signal has important roles in lymphopoiesis and T cell responses. In addition, IL-7Ra expression is dynamically regulated to tune into functional requirements in different cell types. Whereas IL-7Ra is not expressed on hematopoietic stem cells (HSCs), it is an important marker protein for HSC-derived common lymphoid progenitors (CLPs). IL-7Ra expression is maintained while CLPs differentiate to pro-B cells, but is turned off in immature B cells in bone marrow and mature B cells in the periphery. During thymocyte development, the most immature double negative thymocytes express IL-7Ra, but double positive thymocytes do not. IL-7Ra expression is upregulated again in single positive CD4+ and CD8+ thymocytes and maintained on naive T cells in the periphery. Upon encountering foreign antigens, naive T cells are activated and become effector T cells accompanied by down-regulation of IL-7Ra. After the antigens are cleared, a portion of effector T cells give rise to long lasting memory T cells with higher expression of IL-7Ra. GA binding protein and PU.1 are known to activate the transcription of IL-7Ra gene, however, little is known about how the dynamic expression changes of IL-7Ra are achieved on a molecular level. This research project aims to identify cis regulatory modules in the IL-7Ra gene locus. Our long-term goal is to further define critical cis regulatory elements and associated factors that contribute to the dynamic regulation of IL-7Ra. Importantly, during lymphocyte development and T cell responses, many genes such as Notch response gene Deltex 1, Wnt effector transcription factors TCF1/LEF1 show synchronized gene expression changes in concert with IL-7Ra. The precise molecular mechanism underlying IL-7Ra gene regulation could be extrapolated to other genes with synchronized expression and thus provides insights into differentiation of HSCs to T and B lineages and transition of naive T cells to effector and memory T cells. This knowledge may have important implications in treatment of immunodeficiency and vaccine/adjuvant designs. SPECIFIC AIM. To identify cis regulatory modules that contribute to the dynamic expression of IL-7Ra during T and B cell development and T cell responses to antigen stimulation. We will use a bacterial artificial chromosome (BAC) containing the entire IL-7Ra locus to generate reporter transgenic mice by inserting a GFP reporter in the first IL-7Ra-coding exon. In combination with Cre recombinase-mediated stochastic recombination using incompatible Lox variants, we will obtain reporter transgenic mice containing systematic deletion of regulatory regions/modules. By establishing as few as 3 transgenic founder lines, we will narrow down a 200 kb regulatory region to 1-2 kb regulatory sequences which can confer the up- or down- regulation of IL-7Ra during differentiation of HSCs to CLPs and B lineage cells, thymocyte development, and T cell responses. PUBLIC HEALTH RELEVANCE: Interleukin-7 receptor a chain (IL-7Ra) is an important cell surface protein that shows dynamic changes accompanying differentiation of hematopoietic stem cells to pathogen combating T and B cells. IL-7Ra also plays critical roles in maintaining homeostasis of naive and memory T cells. This project will generate insights into how IL-7Ra expression changes are tuned into functional requirements in these cells. The knowledge will provide a scientific basis for manipulating outcomes of hematopoietic stem cell differentiation and immune responses, which is important for understanding T cell malignancy, designing gene-therapy of defective T cell development or function, and formulating more effective vaccines and adjuvants.